A damper operates in vehicle suspensions as a damping device controlling the sprung (body), and unsprung (wheels), masses of a vehicle by reducing loads or vertical accelerations normally transmitted from the wheels to the body. Damping is accomplished by converting kinetic energy into thermal energy and dissipating the heat. Conventionally, hydraulic dampers include a piston with a connected piston rod slidably carried in a fluid-filled tube and separating the tube into extension and compression chambers. A rod guide at the top end of the tube closes the extension chamber and slidably engages the piston rod. The piston rod and the tube are provided with attachment fittings for connection to the sprung and unsprung masses. Due to the operating environment of the damper, the fittings must be securely connected to withstand the applied forces.
Often, the attachment fitting connected to the tube is secured by a welding process since this can be accomplished during the initial stages of assembly when the tube is dry, prior to the addition of hydraulic fluid. The attachment fitting connected to the piston rod is generally secured by a threaded joint. This is because the piston rod fitting is attached after the damper is assembled and filled with oil, since assembly of the damper's internal components requires access over the end of the rod. At this point, the damper may also carry a gas charge. Completing the threaded joint requires threading the rod's end, threading a matching component to be joined to the attachment fitting, mounting that component to the attachment fitting without deforming the threads, and assembling the two threaded parts. This process is undesirably costly.
Generally, it is known that a welded joint is an alternative to a threaded joint. Complications in welding a piston rod fitting to a substantially assembled damper exist. The joint is not amenable to resistance welding since axial loads on the rod of several hundred pounds would be required. Application of that magnitude of welding force is not possible without machining undesirable notches in the rod. Accordingly, a way of welding an attachment fitting to a piston rod that is assembled in a damper tube is required.